1. Field of the Invention
The present invention relates to ducting arrangements for carrying fresh and/or air conditioned air within underground mines and tunnels.
2. Description of the Related Art
Ventilation ducts are used in carrying fresh and/or air conditioned air to work locations in underground mines and tunnels such as coal mines and mines containing precious metals including silver and gold. As in buildings, the ducts are typically installed against the ceiling of the mine or tunnel so that they are out of the way of human and vehicles traveling through and working in the mine or tunnel. As opposed to ducts in buildings, however, which are typically made of a rigid material such as sheet metal, ducts in mines or tunnels are often made of a flexible material such as a high strength PVC fabric with a polyester substrate. An advantage of a flexible material is that the duct can conform to the undulations of the roof and walls, which are common in mines and tunnels. Another advantage is that flexible ducts can be easily deflected or compressed in order to accommodate and make room for the passing of machinery and vehicles which may occasionally pass by with minimal or no clearance.
The advantageous flexibility of the duct material may also be a disadvantage in some respects, however. For example, the high pressure of the air carried by the duct may cause the flexible duct to tend to take on a circular cross-sectional shape, rather than a more desirable rectangular shape or oval shape. A rectangular-shaped or oval-shaped duct may conform better to the flat ceiling and narrow entry widths of the mine/tunnel, and may thereby stay more out of the way of vehicles, humans and machinery that travel and operate within the mine/tunnel.
What is neither disclosed nor suggested in the conventional art is a flexible ventilation duct that can maintain a low-profile cross-sectional shape when carrying a high pressure flow of air or other gas.